Decomposition of materials within a landfill produces landfill gas which contains methane. In some instances, the methane concentration and volume are sufficient to warrant recovery of the landfill gas so that the methane can be used as a fuel. To increase the concentration of methane, a landfill gas purification plant can be installed at the landfill.
The recovery of landfill gas requires a substantial investment for the construction of landfill gas recovery wells. Landfills are not homogeneous and do not produce landfill gas at the same rate at all locations within the landfill. Accordingly, the selection of each landfill gas well site is very important in order to maximize gas production and to minimize the number of wells which cannot be used, or cannot be used for long periods, due to inadequate production.
One method of locating landfill gas wells is described in Johnson et al U.S. Pat. No. 4,026,355. Although this method has been used for many years, it would be desirable to have a lower cost method for locating wells at the best possible sites.
Landfill gas is produced by the landfill at a positive pressure. This positive pressure causes some of the landfill gas to flow upwardly to the upper surface of the landfill and vent to the atmosphere. Another way to locate sites for landfill gas wells is to measure the venting rate of the landfill gas in various regions of the landfill. Common assignees copending application Ser. No. 410,311 filed Aug. 23, 1982 now U.S. Pat. No. 4,444,041, and naming Stanley W. Zison as the inventor describes a novel method and apparatus for measuring the flow of landfill gas from a surface.
Historically the most common form of landfill gas well is a deep well that extends for very substantial distances into the refuse of the landfill. Recently it has been proposed to employ a shallow well located near the top of the refuse in the landfill and to allow the positive pressure of the landfill gas to bring the gas to the well. This eliminates the need for boring deep wells, and because over a long period of time the generation rate of landfill gas equals the venting rate, the collection efficiency of a broad surface collector or shallow well is quite good.
The techniques developed heretofore for locating landfill gas wells and determining their collection rates have been directed primarily to the deep landfill gas well. For example, Johnson et al U.S. Pat. No. 4,026,355 referred to above deals entirely with deep wells. Similarly, although Zison application Ser. No. 410,331 referred to above deals with establishing landfill gas venting rates, it is not specifically directed to locating surface collectors or to determining the collection rate of a surface collector.